1. Field of the Invention
The present invention relates to an impeller for a water pump in which a metal boss is insert-fitted into the rotating center portion of the impeller main body, and the area of the rotating center portion facing the impeller main body is fashioned to an adequate thickness, with the metal boss securely fitting into the impeller main body.
2. Description of the Related Art
Metal bosses, which are used in water pumps installed in water-cooled internal combustion engines for vehicles and the like, are insert-fitted into the rotating center portions of impellers composed of synthetic resin. In other words, a metal boss member is fitted by cast-molding when a synthetic resin impeller is molded. Such impellers for water pumps comprising a synthetic resin impeller main body and a metal boss member have been proposed with the metal boss member having various configurations to provide adequate conditions for metal boss inserts.
The boss member disclosed in Japanese Patent Application Laid-open No. H06-129395, for example, has a square column-shaped peripheral member and an undercut (grooved) member, the perimeter member thereof annularly grooved; has rotation stopped in the direction of rotation by the square column-shaped perimeter member, and slipping-off prevented in the axial direction by the undercut member; and good retention in the insert is obtained thereby.
Moreover, the boss member recited in Japanese Patent Application Laid-open No. H09-217699 has a cylindrical body and a polygonal protruding member formed on the center portion in the width direction around the outside of the cylindrical body; has rotation stopped in the direction of rotation by the polygonal protruding member, and slipping-off prevented in the axial direction; and good retention in the insert is obtained thereby.
The impeller main body for a water pump with a metal boss member insert molded from synthetic resin is configured such that a metal boss member is inserted into the resin, and a detent such as the perimeter of a square column (Japanese Patent Application Laid-open No. H06-129395), a polygonal protruding member (Japanese Patent Application Laid-open No. H09-217699) or the like is formed in the direction of rotation. The impeller main body is fixed to the shaft by the press-fitting of the boss and the shaft.
The stress loads from the boss member on the rotating center portion of the impeller main body molded from synthetic resin is exerted as a result of this press-fitting. For example, the insertion stress load generated when a shaft is press-fitted into a boss, or the plastic deformation of the metal boss member after the shaft has been press-fitted makes it difficult for the resin portion of the rotating center portion of the impeller main body molded from synthetic resin to sufficiently bear residual stress load or another load affecting the resin portion, adversely affecting the durability of the synthetic resin rotating center portion.
To solve such problems, the thickness of the boss mount member in the rotating member of the impeller main body may be increased, but the impeller main body would increase in size as the rotating center portion becomes larger. Furthermore, if the size of the impeller main body remains the same, then the thickness of the resin portion would be reduced and the load on the rotating center portion would further increase. Due to these facts, it is very difficult to provide an impeller with a limited size.
Lowering the press-fitting load of the boss and the shaft may reduce the effect on the resin portion, but the boss member and the shaft cannot be securely fixed and it becomes difficult to stabilize the attachment to the shaft that drives the impeller main body. Because an impeller for a water pump is used in locations in which changes in the outside temperature environment are stringent, it is difficult for the resin portion to sufficiently bear such conditions if the thickness of the boss member fitting location on the rotating center portion of the impeller main body decreases due to the thermal stress load generated by the difference in the coefficient of linear expansion between the resin impeller main body and the metal boss member.
Thus, for various reasons, the thickness of the resin portion in the rotating center portion of the impeller main body cannot be adjusted to a level at which the resin portion has the same strength as the metal boss member. In other words, in the limited range of the edge periphery in the axial direction of the rotating center portion, it is difficult to use a weakened boss member by reducing the thickness of the boss member, which is the core metal of the impeller main body. Consequently, the resin portion of the rotating center portion must be fashioned in accordance with the boss whose strength is maintained in this manner. It is, however, difficult to increase the thickness of the resin portion under this condition, and the resin portion of the rotating center portion becomes thinner than the boss as a result.
Based on these facts, it is difficult to satisfy the strength and durability conditions of the impeller main body composed of synthetic resin and provided with an inserted metal boss member. An object of the present invention is to provide an impeller for a water pump wherein an impeller main body composed of synthetic resin can be securely fixed to the shaft, and a metal boss member can be insert-fitted into the impeller main body composed of synthetic resin without any adverse effect on the strength of the impeller main body or the strength and durability of the impeller in a stringent operating environment.
As a result of earnest investigation conducted in view of the above situation and aimed at addressing the aforementioned problems, the inventors perfected the present invention upon discovering that the aforementioned problems can be addressed by providing an impeller for a water pump comprising an impeller main body composed of synthetic resin and provided with a vane member formed around a rotating center portion, and comprising a metal boss in which a circular boss member positioned on the forward side of the above-mentioned rotating center portion and provided with a gradually narrowing portion at the axial end thereof, and a periaxial support boss member positioned on the rearward side of the rotating center portion are consecutively formed in the axial direction, and in which an axial support surface is formed between the above-mentioned circular boss member and periaxial support boss member; the metal boss insert-fitted into the above-mentioned rotating center portion; and the periaxial support boss member provided with a detent on the external periphery of the axial end portion thereof, whereby the metal boss is insert-fitted into the rotating center portion of the impeller main body, allowing the thickness in the rotating center portion of the impeller main body to be sufficiently obtained, and the metal boss to be very securely fitted to the impeller main body.